1. Field of the Invention
The present invention relates to a novel process for producing methacrylic acid from acetone and methyl formate, or from acetone, methanol and carbon monoxide as starting materials.
Methacrylic acid is an extremely important intermediate in industrial use since it is employed in great quantities as a starting material not only for the synthesis of methyl methacrylate but also for the production of various higher esters.
2. Description of the Related Arts
As the process for industrially producing methacrylic acid, (1) the acetonecyanohydrin process in which prussic acid and acetone are used as starting materials and methacrylic acid is produced through acetonecyanohydrin (hereinafter referred to as "ACH") formed from the abovementioned starting materials, and (2) the C.sub.4 oxidation process in which isobutylene or tert-butanol is used as a starting material have been put into practical application.
Although there have been proposed a number of processes for producing methacrylic acid in addition to the aforementioned processes such as oxidation-dehydrogenation of isobutyric acid, condensation-dehydration of propionic acid or propionaldehyde and formaldehyde, etc., none of them has yet been put into practice.
The ACH process is a process in which ACH is synthesized from prussic acid and acetone, and then the resultant ACH is reacted with water in the presence of sulfuric acid to produce methacrylic acid.
The ACH process has been widely carried out by virtue of its easy reaction and high yields, but suffers the disadvantage that large amounts of waste sulfuric acid and ammonium sulfate are by-produced and the treatment thereof increases the production cost of methacrylic acid.
On the other hand, the above-mentioned C.sub.4 oxidation process suffers from the defects that a number of side reactions take place lowering the yield of methacrylic acid, purification costs are high, a complicated and expensive production plant is required, and the supply of isobutylene or tert-butanol to be used as the starting material is limited.
An intensive research made by the present inventors on the process capable of producing methacrylic acid at an inexpensive cost with easy and stable supply of starting materials finally led to success in accomplishing the present invention.